RICERCA ITALIANA     

Research program

Contribution to atmospheric CO2 mitigation at the point source

University Co-ordinator

Università degli Studi di ROMA "La Sapienza" - SCIENZE DELLA TERRA - ()

Research Unit Leader

Vincenzo Ferrini

Description

The aim of the research program is to develop a carbonation process by the synthesis of the hydrated precursors of magnesite (nesquehonite and hydromagnesite) instead of the direct precipitation of magnesite. The main advantages of this process route are its simple process design and the opportunity to realize the carbonation process under conditions of room temperature and atmospheric pressure. This approach for a carbonation process is due to two main reasons: a) under atmospheric conditions the precipitation of hydrated carbonates is thermodynamically favoured with respect to that of magnesite; b) the stability conditions of the hydrated magnesium carbonates are consistent with a safe and long-term storage of CO2 as the sequestration of the carbon dioxide in these minerals is stable up to about 500°C.
The mineral carbonation process will be carried out in water using MgCl2 solutions. The experiments will be executed according to two stages. The first set of tests will be aimed at the study of the carbonation reactions, whereas the second set of experiments will be focused on the collection of data for optimising the process design for its industrial development.
The first set of experiments will be carried out during the first year under conditions of room temperature and atmospheric pressure. The magnesium chloride solutions will be obtained using MgCl2·6H2O in 200 mL deionised water. The solutions will be agitated vigorously (300-400 rpm) with a magnetic stirrer. The CO2 will be sparged through the solution while stirring continuously. The influence of the Mg concentration and CO2 flux will be investigated by using solutions with various Mg concentrations and varying the carbon dioxide flux in the range 20-200 mL/min. Moreover, the time of the reaction between the solution and CO2 will be varied between few minutes and some hours to evaluate the kinetics of the carbonation reaction.
During the experiments the pH will be measured before sparging the CO2 and at the end of the reaction time. The influence of solution pH on the resulting products will be investigated carrying out the experiments in a pH range suitable for the formation of the hydrated magnesium carbonates. After the reaction period the solution will be filtered using Nucleopore membranes and the solid products will be washed with deionised water. The solid products will then dried at 105-110°C. In order to determine the mineralogical components and their crystallinity, the solid products will be studied by XRD. Moreover, FTIR and SEM-EDS analyses of the solid products will be performed. The residual Mg contents in the solutions will be determined by ICP-AES to obtain information about the rate of carbonation.
The results of this set of experiments will be used to evaluate the efficiency of the carbonation process and to plan the experimental work that will be carried out during the second year of the research. The second set of experiments will be executed according to the above procedure, but applying some variations of the parameters that mainly control the kinetics of the carbonation reactions. These experiments will be carried out in reactors and the operating conditions will be varied up to 150°C and 20-30 bars of CO2. The main objective of this set of experiments will be to obtain information useful to optimise the reactions of the mineral carbonation with respect to temperature and pressure conditions, composition of the solutions, flux of CO2 and application of additives. In this view, NaCl and NaHCO3 have been used in aqueous carbonation studies. Medina et al. (2000) have showed that an increase of the hydration of CO2 could enhance the carbonation rate. A useful additive for this could also be the enzyme carbonic anhydrase (Simsek-Ege et al., 2001) that might accelerate the process.